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Bipedally trained rats have an increased hindlimb muscle force‐generating capacity compared to quadrupedally trained rats
Author(s) -
Eng Carolyn,
Reed Andrew,
Foster Adam
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.865.1
Subject(s) - muscle architecture , sarcomere , hindlimb , quadrupedalism , anatomy , muscle mass , muscle fibre , fiber , treadmill , physical medicine and rehabilitation , skeletal muscle , biology , medicine , chemistry , physical therapy , myocyte , organic chemistry
The shift from bipedalism to quadrupedalism in human evolution led to major morphological changes because of new demands placed on the locomotor system including include larger forces on each limb. The ability for a muscle to generate forces and length change to respond to these demands depends on the muscle's architecture, or the arrangement of fibers within a muscle. Muscle force is determined by the cross‐sectional area of its fibers (physiological cross‐sectional area or PCSA), while muscle excursion is determined by fiber length.
In this study, we asked whether changes in muscle architecture respond to the demands of bipedal locomotion and if this response can occur during the lifetime of an individual. To test this question, we trained rats to stand or walk bipedally on a treadmill for one hour a day for five days a week over 90 days using a harness that loaded the hindlimbs to 90% of body mass. A control group was trained quadrupedally over the same time period. The rats were sacrificed and their hindlimbs were fixed in formalin. Muscles were dissected from one hindlimb each of the bipedally (BI) and quadrupedally trained rats (QU). Measurements of muscle mass, length, fiber length, sarcomere length, and pennation angle were obtained and used to calculate normalized fiber length and PCSA. PCSA was normalized to body mass.
We found an increase in the mass‐specific PCSA of muscles in the BI rats compared to QU rat muscles. Furthermore, the larger PCSA in BI rats was achieved through a decrease in fiber length as opposed to an increase in muscle mass. These results indicate that muscle architecture responds to the varied demands of bipedal locomotion and these changes are a plastic response that can occur over a short time period.